Device and method for use in the verification of handwriting

Abstract

A device ( 10 ) for use in the verification of handwriting, comprising: a body ( 12 ) having a surface ( 11 ) over which a writing instrument ( 8 ) is moved during the generation of a piece of handwriting; a transducer ( 14 ) for transducing stress-wave activity in the body ( 12 ) to an analogue time varying signal ( 15 ); and digitizing means ( 22 ) for converting the analogue time varying signal ( 15 ) into a digital signal ( 27, 31, 11 ), the digitizing means ( 22 ) comprising a sampler ( 22 ) arranged to under-sample the analogue time varying signal ( 15 ).

1. A device for use in the verification of handwriting, comprising:
 a body having a surface over which a writing instrument is moved during the generation of a piece of handwriting; 
 a transducer for transducing stress-wave activity in the body to an analogue time varying signal, and; 
 characterised by digitizing means for converting the analogue time varying signal into a digital signal the digitizing means comprising a sampler arranged to under-sample the analogue time varying signal. 
 
   
   
     2. A device as claimed in  claim 1 , wherein the sampler operates at a sample frequency substantially less than a sample frequency specified by Nyquist's criterion. 
   
   
     3. A device as claimed in  claim 1  wherein the analogue time varying signal is a modulated carrier signal having substantially a carrier frequency. 
   
   
     4. A device as claimed in  claim 3 , wherein the carrier frequency is in the region of 100 kHz. 
   
   
     5. A device as claimed in  claim 2 , wherein the sample frequency is less than 20 kHz. 
   
   
     6. A device as claimed in  claim 1 , further comprising means for dc offsetting the digital signal. 
   
   
     7. A device as claimed in  claim 1 , further comprising means for rectifying the digital signal. 
   
   
     8. A device as claimed in  claim 1 , wherein the digital signal includes a set of binary words and the digitizing means further comprises means for independently varying the binary words. 
   
   
     9. A method of forming a digital signal from an analogue signal representing stress-wave activity produced during a piece of handwriting, comprising the step of: under-sampling the analogue signal to form the digital signal wherein the step of under-sampling comprises sampling the analogue signal at a first frequency substantially less than its highest frequency component. 
   
   
     10. A method as claimed in  claim 9 , wherein the analogue signal is a modulated carrier signal and the highest frequency component of the analogue signal is the frequency of the carrier signal. 
   
   
     11. A method of forming a digital signal from an analogue signal representing stress-wave activity produced during a piece of handwriting, comprising the steps of:
 under-sampling the analogue signal to form the digital signal and; 
 dc offsetting the digital signal. 
 
   
   
     12. A method as claimed in  claim 9 , further comprising the step of: rectifying the digital signal. 
   
   
     13. A system for use in the verification of handwriting, comprising: a transducer for transducing stress-wave activity, arising when a writing instrument is moved during the generation of a piece of handwriting to an analogue time varying signal and; characterised by digitizing means for converting the analogue time varying signal into a digital signal, the digitizing means comprising a sampler arranged to under-sample the analogue time varying signal. 
   
   
     14. A system as claimed in  claim 13 , further comprising a body having a surface over which the writing instrument is moved, wherein the transducer is associated with the body. 
   
   
     15. A system as claimed in  claim 13 , further comprising a body having a surface over which the writing instrument is moved, wherein the transducer is separate from the body and the writing instrument. 
   
   
     16. A system as claimed in  claim 13 , further comprising a writing instrument comprising the transducer.